1. Field of the Invention:
This invention relates generally to dynamoelectric machines, and more particularly to such machines which have a radially ventilated rotor.
2. Statement of the Prior Art:
It is well known that the conductors forming electrical windings in dynamoelectric machines can be cooled by passing a cooling fluid through the windings, which are contained within longitudinally extending slots that are radially disposed about the periphery of a rotor of the machine, in direct contact with the material of the conductors. One form of cooling common in generators for power station use is radial cooling in which the cooling fluid is caused to flow in a radial direction with respect to the central axis of the generator, through radially disposed ducts formed in the conductors of each slot.
In U.S. Pat. No. 4,508,985, which is assigned to the assignee of the present invention and is incorporated herein by reference, the general characteristics of machines with radial path air-cooled rotors are described as they have been made heretofore, as well as an improvement thereto for providing better flow into the slot channels by means of a channel inlet fairing. This provides better cooling of the rotor so that machine size and noise can be reduced.
In machines with such radial air cooling of the rotor in accordance with the prior art, the air is supplied to the end turn region through a stationary inlet duct that extends substantially radially from the periphery of the machine. The air then flows radially inward from the inlet duct, entering the interior to the retaining ring and field winding end turns and flowing in the axial direction with little or no tangential velocity component. Part of the air flows radially outward, cooling the end turns and exists the retaining ring through ventilation holes. The remaining air passes into the field winding slot channels and hence radially outward through a number of slits in the field winding, cooling the body portion of the winding. The air then exists through radial holes in the rotor wedges and enters the air gap. Air from the body portion of the winding flows axially and circumferentially along the air gap and joins the air from the end turn portion of the winding. This combined exhaust flow then is dumped interior to the machine enclosure and exits through the cooler where heat is removed. The air then continues to recirculate.
In U.S. Pat. No. 4,547,688, which is also assigned to the assignee of the present invention and is incorporated herein by reference, the flow path is improved by modifying the inlet duct configuration to include means for rotationally directing coolant out of said duct in the direction of the rotation of the rotor. This means comprises, for example, a plurality of inlet guide vanes in fixed locations between axially inner and outer walls of the inlet duct. The guide vanes are each member extending substantially the entire distance between the walls of the duct proximate the end of the inlet duct adjacent the end turns. They are on an angle relative to a direct radium from the shaft axis so that their radial lower edge is circumferentially spaced from their upper edge in the direction of rotor rotation. Preferably, each of the inlet guide vanes has an airfoil configuration with smoothly curved major surfaces between their upper and lower edges and those edges are smoothly rounded. The vanes may take other forms so long as they impart a tangential velocity to the coolant as it leaves the inlet duct.
It is also well known, however, that dynamoelectric machines having radially ventilated rotors, such as those machines described above with reference to U.S. Pat. No. 4,508,985 and U.S. Pat. No. 4,547,688, experience a "siren effect" due to the flow noise produced by the fluid flow into the periodic channels. Such a "siren effect" is highly undesirable in circumstances where low noise is of importance, such as in shipboard machines. The apparatus of U.S. Pat. No. 4,547,688 reduces such effects by matching the air tangential speed with the subslot inlet speed in order to reduce chopping of the air by the subslot inlets. Nevertheless, neither the apparatus of U.S. Pat. No. 4,508,985 not the apparatus of U.S. Pat. No. 4,547,668 addresses the problem of flow noise induced by the absence of fluid flow from the pole regions of a rotor.
The cooling paths formed in prior art radially ventilated rotors, as is evident, only provide a flow of the fluid out of the rotor in the vicinity of the slots containing the field winding conductors. In regions about the periphery of the rotor between the field winding conductors, such as in the pole regions of the rotor, substantially no flow is present. Accordingly, a non-uniform flow distribution is set up circumferentially about the periphery of the rotor such that a "flow-no flow" condition exists. This "flow-no flow" condition further leads to the production of undesirable noise components as the non-uniform flow distribution impinges upon the stationary parts of the dynamoelectric machine.